US 8134492 B1 Abstract A radar volume in a cued direction is searched with sequential pencil beams. The allowable scan time is limited. The cued direction and uncertainty identify a search face, and the range gives a search volume. The number of beams required to scan the volume is determined, and compared with the maximum time. If less than the maximum, the scan is initiated. If greater than the maximum time, the scan region about the cued volume is subdivided into smaller portions, each of which is scanned sequentially.
Claims(18) 1. A method for searching an angular region of a radar search volume about a given cued direction and with a maximum range, where the search of the radar search volume is performed with sequentially applied radar beams having defined beamwidths, said method comprising the steps of:
acquiring error information;
from said error information, determining azimuth and elevation extents of a search face of the radar search volume about the cue direction;
determining an angular extent of each of a plurality of radar beams in azimuth and elevation;
from said angular extents in azimuth and elevation for each radar beam, determining a number of beams required to cover the search face of the radar search volume;
determining a dwell time for each of the radar beams given the maximum range;
taking a product of said number of beams multiplied by the dwell time per beam to obtain a search time;
comparing said search time with a maximum allowable search time;
initiating radar scanning over said search face with said number of beams if said search time is less that said maximum allowable search time; and
partitioning said search face into sub-search-faces if said search time is greater than said maximum allowable search time, and for each of said sub-search-faces, initiating radar scanning;
wherein said step of determining the number of beams required to cover the search face includes the calculation of
where:
A
_{ext }is half the azimuth extent of the search face;E
_{ext }is half the elevation extent of the search face;ΔA is the azimuthal beam separation at constant elevation;
ΔA=(β/2)cos α, where β is the beam width and α is equal to ½ the acute angle of the two lines that extend from the center of a radar beam to the points of intersection of the circumference of the beam with the circumference of an adjacent beam;
ΔE is the elevation separation of the line of centers of the horizontal rows;
ΔE=(β/2)(1+sin α); and
flr is a floor function that truncates the argument to the highest integer less than the argument.
2. The method of
3. The method of
4. The method of
5. The method of
6. The method of
7. A system for searching an angular region of a radar search volume, said system comprising:
a command and decision unit for:
determining azimuth and elevation extents of a search face of the radar search volume about a cue direction from error information; and
determining an angular extent of each of a plurality of radar beams in azimuth and elevation; and
a radar beam controller for:
from said angular extents in azimuth and elevation for each radar beam, determining a number of beams required to cover the search face of the search volume;
determining a dwell time for each of the radar beams given a maximum range;
taking a product of said number of beams multiplied by the dwell time per beam to obtain a search time;
comparing said search time with a maximum allowable search time;
initiating radar scanning over said search face with said number of beams if said search time is less that said maximum allowable search time; and
partitioning said search face into sub-search-faces if said search time is greater than said maximum allowable search time, and for each of said sub-search-faces, initiating radar scanning.
8. The system of
where:
A
_{ext }is half the azimuth extent of the search face;E
_{ext }is half the elevation extent of the search face;ΔA is the azimuthal beam separation at constant elevation;
ΔA=(β/2)cos α, where β is the beam width and α is equal to ½ the acute angle of the two lines that extend from the center of a radar beam to the points of intersection of the circumference of the beam with the circumference of an adjacent beam;
ΔE is the elevation separation of the line of centers of the horizontal rows;
ΔE=(β/2)(1+sin α); and
flr is a floor function that truncates the argument to the highest integer less than the argument.
9. The system of
10. The system of
11. The system of
12. The system of
13. The system of
14. A method for searching a portion of a radar search volume, said method comprising the steps of:
determining azimuth and elevation extents of a search face of the search volume about the cue direction from error information;
determining an angular extent of each of a plurality of radar beams in azimuth and elevation;
from said angular extents in azimuth and elevation for each radar beam, determining a number of beams required to cover the search face of the radar search volume;
determining a dwell time for each of the radar beams given a maximum search range of said plurality of radar beams;
obtaining a search time by multiplying said number of beams by the dwell time per beam;
comparing said search time with a maximum allowable search time;
initiating radar scanning of the search face if said search time is less than said maximum allowable search time; and
reducing a size of said search face if said search time is greater than said maximum allowable search time, and for said reduced size search face, initiating radar scanning.
15. The method of
where:
A
_{ext }is half the azimuth extent of the search face;E
_{ext }is half the elevation extent of the search face;ΔA is the azimuthal beam separation at constant elevation;
ΔA=(β/2)cos α, where β is the beam width and α is equal to ½ the acute angle of the two lines that extend from the center of a radar beam to the points of intersection of the circumference of the beam with the circumference of an adjacent beam;
ΔE is the elevation separation of the line of centers of the horizontal rows;
ΔE=(β/2)(1+sin α); and
flr is a floor function that truncates the argument to the highest integer less than the argument.
16. The method of
17. The method of
18. The method of
Description SPY is a naval radar system which searches space under control of command and decision processing. It searches by means of a plurality of sequential directional beams which may be pointed in a given direction. Command and Decision determines the acquisition face (volume) to be searched. The radar beam is directed to each angle so as to cover the entire search face. This type of searching is subject to time constraints, as the beam must dwell at the current beam angle for a sufficient time for the transmitted radar signals or pulses to travel to the target, which might be at the maximum allowable range, and for the reflection to return to the radar. The round-trip time is the well-known 12.4 microseconds per mile of target range. Thus, the beam must dwell at each angle of the search face for a sufficient length of time to detect a target at the maximum range, and then move on to the next angle within the search beam pattern. Because of the need to keep the radar system in use, as when searching multiple volumes in the case of multiple potential targets, it is necessary to limit the amount of time spent searching a given volume. The system aborts the search of a volume of space after a given time. Consequently, a search through a volume of space may be initiated and aborted without being completed. This operation may result in a failure to locate a target within the specified scan volume. In order to avoid having a scan aborted and the resulting problems, it is imperative that the searching of any given volume be performed in the least possible time. The Spy radar can operate in a volume search mode. When information becomes available from another source, such as a cooperating radar, about the possible presence of a target in a nominal given direction or location, it may be desired to examine a volume about the nominal given direction in an attempt to acquire the target. This is termed a “cued” search. If the selected volume is too large, the search may time-out before completion of the search, and if too small, may not find the relevant target(s). Improved or alternative arrangements are desired for establishing the angular extent of the search volume about the cued nominal direction of a target to guarantee that the search can be accomplished within given time constraints. A method according to an aspect of the invention is for searching an angular region of the radar acquisition or search volume about a given cued direction and with a given maximum search range. The radar search of the designated volume is performed with sequentially generated radar beams having defined beamwidths. The method comprises the steps of acquiring the nominal track position and velocity (cue information) and time, and error information describing the uncertainty in the cue information. This error information may be presented together with the cue information. From the error information, the azimuth and elevation extent (the acquisition or search face) of the search volume about the cue direction is determined. If necessary, the angular extent of each beam in the azimuth and elevation directions are determined from the beamwidths. From the angular extents in azimuth and elevation for each beam, the number of beams required to cover the acquisition face is determined [equation 1]. The dwell time for each of the beams is determined from the search range. The search time is determined as the product of the number of beams multiplied by the dwell time per beam. The search time is compared with the maximum allowable search time, and radar scanning over the acquisition face is initiated with the calculated number of beams if the search time is less than the maximum allowable search time. The acquisition or search face is partitioned into sub-search-faces if the search time is greater than the maximum allowable search time. Sequential radar scanning of each of the sub-search-faces is initiated. In a preferred mode of the method, the number of beams N is calculated as A E ΔA is the azimuthal beam separation at constant elevation; ΔA=(β/2)cos α, where β is the beam width and α is derived from the beam placement pattern, and is typically equal to 30 degrees. More specifically, α is equal to ½ the acute angle between the two lines that extend from the center of a radar beam to the points of intersection of the circumference of the beam with the circumference of an adjacent beam; ΔE is the elevation separation of the line of centers of the horizontal rows; ΔE=(β/2)(1+sin α); and flr is a floor function that truncates the argument to the highest integer less than the argument. Prior arrangements for determining the number of beams required in a fixed pattern about the cued direction have tended to give numbers that, in some cases, were greater than desired. As a result, the cued searching of the radar in these cases might exceed the maximum search time, thereby causing the search to be aborted. In the scenario In The target azimuth and elevation relative to ownship The radar beam controller It should be understood that the number of pencil beams can be selected somewhat arbitrarily, in order to cover the desired acquisition face That is, due to unavoidable errors in determining the exact location of the target, and due to errors in determining the direction in ownship local coordinates, the target may not be found at the precise specified cue coordinates. In order to acquire and track the target with ownship radar, it is desirable to search a region or extent about the nominal target local coordinates. Thus, the search or acquisition face to be searched by ownship radar to acquire target The SPY radar places an initial search beam designated According to an aspect of the invention, the azimuth extent A By extension, letting parameter n the floor (flr) function truncates the argument to the highest integer less than the argument; and ΔA is the spacing between beams in the azimuth direction. For all remaining horizontal beam lines, e.g. those centered at ±ΔE, ±3ΔE, . . . , of
Equations (5) and (7) hold also in elevation, with the simple change of E According to an aspect of the invention, the number N of beams required to cover acquisition face is given by A E ΔA is the azimuth separation of the line of centers of adjacent horizontal columns; ΔE is the elevation separation of the line of centers of adjacent horizontal rows; ΔE=(β/2)(1+sin α); flr is a floor function that truncates the argument to the highest integer less than the argument; and ΔA=(β/2)cos α, where β is the beam width of a single beam and α is equal to ½ the acute angle between the two lines that extend from the center of a radar beam to the points of intersection of the circumference of the beam with the circumference of an adjacent beam. In As mentioned, ΔA is the azimuthal (horizontal) distance between beam centers of adjacent beam columns, that is, between the center of a beam and the center of the adjacent beam in the row above or below, and not between beam centers in a given row. Similarly, ΔE is the elevation (vertical) distance between beam centers of adjacent rows, i.e. between the center of a beam and the center of the adjacent beam in the row above or below it. In the representative acquisition face of As can be observed by counting beams in Block If decision block Block A method according to an aspect of the invention is for searching an angular acquisition region ( A E ΔA is the azimuthal beam separation at constant elevation; ΔA=(β/2)cos α, where β is the beam width and α is [derived from the beam placement pattern according to well-known art, typically equal to 30 degrees]; ΔE is the elevation separation of the line of centers of the horizontal rows; ΔE=(β/2)(1+sin α); and flr is a floor function that truncates the argument to the highest integer less than the argument. Patent Citations
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